1. Field of the Invention
The present invention relates to a method of fabricating a light-scattering substrate, a light-scattering substrate fabricated by the same method, and an organic light-emitting device (OLED) including the same light-scattering substrate, and more particularly, to a method of fabricating a light-scattering substrate, a light-scattering substrate fabricated by the same method, and an organic light-emitting device including the same light-scattering substrate, in which a light-scattering layer of the light-scattering substrate can improve a light extraction efficiency.
2. Description of Related Art
Organic light-emitting devices (OLEDs), such as organic light-emitting diodes, are self-light-emitting devices each of which has a light-emitting layer situated between two electrodes. Specifically, OLEDs emit light in response to the transition of excitons from an excited state into a ground state. The excitons are generated through the combination of electrons injected through a cathode, or an electron injection electrode, and holes injected through an anode, or an hole injection electrode. OLEDs can have a double-layer structure which includes a hole transport (injection) layer and an electron transporting light-emitting layer or a triple-layer structure which includes a hole transport (injection) layer, a light-emitting layer and an electron transport (injection) layer.
Organic light-emitting displays each including OLEDs are divided into a passive matrix type and an active matrix type depending on the mechanism that drives an N*M number of pixels which are arranged in the shape of a matrix.
In the active matrix type, a pixel electrode which defines a light-emitting area and a unit pixel driving circuit which applies a current or voltage to the pixel electrode are positioned in a unit pixel area. The unit pixel driving circuit has at least one thin-film transistor (TFT) and one capacitor. Due to this configuration, the unit pixel driving circuit can supply a constant current regardless of the number of pixels, thereby realizing uniform luminance. In addition, the active matrix type organic light-emitting display consumes little power, and thus can be advantageously applied to high definition displays and large displays. The passive matrix type has a simpler structure than the active matrix type since it induces a current directly to each pixel. However, the passive matrix type is typically used in small displays and for illumination, since it is not suitable for large high-resolution displays.
In OLEDs, when electrons and holes recombine in the light-emitting layer, the possibility of the generation singlet excitons is limited due to the dependence of the spin statistics. Therefore, the maximum luminous efficiency of OLEDs is merely about 25%.
In addition, in OLEDs, light loss is caused by total reflection at the interface between a thin-film layer and a substrate of each OLED. Thus, the actual light extraction efficiency is merely about 20%, which is problematic.
Accordingly, a variety of studies are underway in order to improve the low light extraction efficiency of OLEDs.
In particular, methods of coating a substrate with a light-scattering layer which includes scattering particles are generally used. Specifically, the light-scattering layer is formed by impregnating metal oxide particles in a matrix material such that the metal oxide particles are used as scattering particles. Then, a light-scattering effect can be obtained at the interface of the metal oxide particles due to different refractive indices.
The light-scattering layer is formed by a wet coating method, such as spin coating or bar coating. According to this method, however, it is difficult to uniformly disperse the metal oxide particles inside the matrix. Due to the characteristics of the wet coating, during the baking of the liquid matrix, the volume of the matrix is reduced by about ⅕ to about 1/20, which is problematic.
The information disclosed in the Background of the Invention section is provided only for enhancement of (or better) understanding of the background of the invention, and should not be taken as an acknowledgment or any form of suggestion that this information forms a prior art that would already be known to a person skilled in the art.